Determination of transport parameters in [EMIm]Cl–based Ionic Liquids – Diffusion and electrical conductivity

The density, electrical conductivity and diffusion coefficients of anions and cations in the ionic liquid AlCl3/1-ethyl-3-methylimidazolium chloride, [EMIm]Cl, were determined to study physical correlations of these important parameters. The density was measured for different molar ratios of AlCl3:[EMIm]Cl from 0.5:1 to 2.0:1 at ambient temperature. The diffusion coefficient of the electrochemically active heptachloroaluminate complex, Al2Cl7−, was measured for a molar ratio of 2:1 in the range of 25°C to 100°C. The corresponding current density and potential transients were discussed regarding the decomposition of the [EMIm]+ cation and deviation from the theoretical Cottrell behavior. The electrical conductivity was measured for molar ratios of 1.5:1 and 2:1 in the range of 25°C to 100°C. Both the diffusion coefficient and electrical conductivity can be described well by an Arrhenius law. The diffusion coefficients of AlCl4−, Al2Cl7− and [EMIm]+ were estimated from the Nernst–Einstein and Stokes–Einstein relation. The results indicate a strong impact of ion pairing in these electrolytes.